The present invention relates to materials and systems for determining at least a condition of components used in a harsh environment, methods of making such systems, and methods for determining such a condition. In particular, the present invention relates to systems for measuring temperature and/or strain of a component used in a hot gas path of a turbine engine, methods of making such systems, and methods for determining temperature and/or strain of such a component.
The operating temperature of gas turbine engines has continually been increased in an attempt to increase their efficiency. Consequently, gas turbine engine components also are exposed to increasingly higher temperatures, which decrease the design margin for the superalloy used to make the engine components. The superalloy substrate of certain engine components, such as combustor or high-pressure fan blades, is typically protected with a thermal barrier coating (or “TBC”) comprising at least a layer of a refractory or thermally insulating material such as yttria-stabilized zirconia (or “YSZ”), which is zirconia stabilized with, for example, about 6–8 percent by weight of yttria. The refractory material would generally be selected to have a low thermal conductivity such as about 1–3 W/(m)(K), thereby reducing heat transfer to and the temperature experienced by the superalloy substrate. A typical thermal barrier coating is a multilayer system comprising at least two layers. In addition to the refractory layer, a bondcoat is applied to the surface of the superalloy of the turbine component. This bondcoat typically comprises an MCrAlY or an MAl alloy wherein M is nickel, and/or cobalt, or PtN alloy. The purpose of the bondcoat is to provide a layer that adheres well to the underlying alloy, provides protection against oxidation of the alloy, and provides a good base for further coatings. An optional intermediate layer or interlayer is applied on the bondcoat. A suitable material for this interlayer is Al2O3. This material can be formed by oxidizing the surface of the bondcoat to form an oxide layer prior to the deposition of the TBC. The interlayer provides improved adhesion for the final thermal insulating YSZ coating and is not included for a thermal barrier property.
Despite great care taken during manufacture to ensure good adhesion of the thermal barrier coating to the underlying material of the turbine component, thermal cycling during use of such a component eventually leads to spalling of the coating. In addition, erosion of the thermal barrier coating is inevitable over an extended period of use. Such a spalling or erosion would eventually expose the underlying bond-coated superalloy to extreme temperatures that would lead to failure of the component. The engine component may be inspected frequently for such a spalling or erosion. However, an inspection entails taking the engine out of service with the attendant cost. Therefore, it is very desirable to know when the underlying superalloy begins to be exposed to extreme temperatures so that appropriate maintenance of the engine is conducted. Wire thermocouples have been embedded in grooves cut into the superalloy substrate and filled with a high-temperature dielectric material to provide temperature measurement. However, this type of thermocouple installation sacrifices component wall thickness and is typically labor intensive because the fabrication process must ensure that the dielectric material and the thermocouple wires remain adhered to the substrate in the long run. Thin-film thermocouples have been deposited on the surface of components used in high-temperature environments to measure the temperature thereof. They are thin enough so as not to significantly disturb the aerodynamics of the component and can rapidly respond to changes in temperature of the surrounding medium. However, these thin-film thermocouples have frequently spalled off because of poor compatibility with the underlying material and defects produced during processing and/or use of the component.
Therefore, there is a continued need to provide reliable systems and methods for measuring temperature of a material used in an environment near its design temperature limit. It is also very desirable to monitor the temperature of such a material from a remote location. Furthermore, it is also very desirable to alert the user when such material begins to experience a temperature outside its intended limit.